function not working properly in loop

[Ennoia]

Hello there, I am beginner in C++, coding for like day or two.
My friend, who insisted, that I should learn how to code, gave me an excercise: make a program with function, that checks, if given number is happy, or not.
I am too green, to be able to check my problem effectively in google, cause I don't really know what keywords I should use. Checked "function in loop c++" and some similars and didn't come to solution. It is probably some very basic mistake, but still - cannot find it ;/
Here is sampled code, that I talk about [in reality code is a little big bigger, cause there is also another function, that checks, if number is happy or not, but error occured even earlier].

#include <iostream>
using namespace std;

int bitdown(int a) /*This is function "break it down", which calculates the sum of squared digits of a number, which is then required to check, if number is happy or not. It works properly, if copied into main function and cin>> any number within int range*/

int b, c=10, d, e=1, f=0, tab[f+1];

while(b!=0)
{
b=a/c; /*loop closes, after it gives 0, this ensures, that you can use number of any size you want*/
d=(a%c)/e; /*gives you digits of number*/
tab[f]=d; //puts these digits into table
f++;
c=c*10;
e=e*10;
}
a=0;
while(f>0)
{
a=a+tab[f-1]*tab[f-1]; //extract digits from table and make sum of squares
f--;
}
return a;
}

int main (int argc, char** argv){ /*main function, where I make test, if function bitdown works properly, if looped*/
int a, b;

cin >> a;

for (b=0;b<3;b++)
{
a=bitdown(a); // test occurs here
cout << a <<endl;
}
return 0;
}

The result I expect for 7 is:
49
97
130.
What I get is:
49
0
0.

I suspect there is some property of language itself, that I don't understand yet, cause when it comes to formal mistakes, like calibraces, comas and other - it seems allright.

Thanks for any help!

[Stalker]

Here is the correct solution:

#include <iostream>
using namespace std;

size_t bitdown(size_t a)
{
    size_t Sum = 0, c;
    while((a / 10) != 0)
    {
        c = a % 10;
        Sum += (c * c);
        a /= 10;
    }
    Sum += a * a;
    return Sum;
}


int main ()
{
    size_t a;
    cin >> a;
    for (size_t b = 0; b < 3; b++)
    {
        a = bitdown(a);
        cout << a << endl;
    }
    return 0;
}

There were very basic errors in your code.

[Ennoia]

Thank you for your version. Indeed it works as intended and you said I made very basic errors. Well, my code is overcomplicated, yours is much more elegant and simple, but as far as I can tell it makes pretty much the same, as mine. Where is the source of my error? I'd rather learn a little, than just use your correct version.

[jlb]

Where is the source of my error? I'd rather learn a little, than just use your correct version.

Good attitude, you'll learn more by writing and fixing your code.

Your first problem is that you appear to have a missing opening brace for your bitdown() function. Also you need to find and consistently use some indentation style, this will make your program much easier to read and troubleshoot. Also you need to "wrap" your long lines to make the information easier to read, try to keep your line lengths reasonable (about 80 characters is considered normal).

https://en.wikipedia.org/wiki/Indent_style

Next once you fix the brace issue you seem to be trying to use a VLA (Variable Length Array), this "feature" is not allowed in a C++ program. The VLA in question is the tab[] array definition, array sizes in C++ must be compile time constants.

After you fix these issues, if you still have problems, post your modified code and any compiler error messages and then ask specific questions about your modified code.

[Stalker]

Like he pointed out your mistakes. And I used your code as a base for mine. So I basically cleaned your code and it looks like this.